[600MRG] Loading coils....

[Kenneth G. Gordon]

OK. I just realized that think I may have a misconception here about 
base-loading coils for verticals.

I have a 55' tall vertical, which was originally designed for the 80 and 40 
meter ham bands. It has a combination trap/loading coil at the 33 foot level, 
so that the antenna acts as a 1/4 wave antenna on both 80 and 40 meters.

I feed it with 50 ohm coax, and use a home-brew antenna coupler at the 
transmitter end to load it on all bands, including WARC bands.

It works very well, considering that it is a vertical.

Furthermore, it is the only antenna I have.

Last year, I added a base "loading coil" to it so I could operate the antenna 
on 160 meters.

I also calculated and bought the necessary "stuff" to make a base-loading 
coil for 600 meters.

Now here's my confusion: when I used the base-loading coil on 160 meters, I 
connected one end of the coil to the antenna, and left the other end 
"floating". I.e., not connected to anything.

Then I tapped down on the coil in the direction away from the antenna until I 
was able to obtain a 1:1 SWR on 160 meters.

This worked quite well, and I managed to work Europe twice with this combo 
and 100 watts on that band.

So, what was actually happening?

What is confusing me is that I THINK I recall seeing base-loading coils 
added to verticals, like for a car, but the "far" end of the coil is grounded, and 
the coax was connected to a tap somewhere above the ground point.

This, to me, means that the coil + antenna must FIRST be resonant at the 
operating frequency, and THEN the tap for the feedpoint must be chosen to 
match the coax impedance.

So, what was happening when I did NOT have the "other" end of the coil 
grounded, yet the system worked very well? 

BTW, it took only about 2 turns of a 4" diameter coil wound of #12 wire on a 
ceramic form to achieve the match.

I now suspect that my antenna coupler was providing the necessary extra 
inductance to enable the match.

In addition, I cannot find my ARRL Antenna Book right now... :-(

Ken W7EKB